Re: missile guidance vs. CNC

Alan Marconett KM6VV wrote:

> Jeff,
>
> I'm not EVEN trying to "straighten you out"! ;>) But I will comment on
> the missile guidance system. I think what you're saying is that
> acceleration in down range and cross range directions is counted, the
> missile is "steered" with the cross range error, and when the missile
> gets to it's "terminal point" (a spot in space from where it can
> "ballistic free fall" on the target), it separates the payload, which
> then "falls" the rest of the way. Does this work for mills? Not sure
> there! I'm already over my head!

No, missile guidance is pretty different from machining. The big difference
is a missile only has to hit the target, it doesn't matter what path it takes
to get there, or how smooth the path is. (It is true that there is not a
great choice of paths due to fuel constraints, etc.) Anyway, the need
to have complete control over the entire contour during the entire
cutting motion of the system is kind of different. (Of course, the
missile really needs tight control of an essentially unstable vehicle
all the time during the boost phase, and that is done by planning a
trajectory, checking error and making fine corrections to get back on
course, so that part is actually not so different.)

Maybe the real difference is that the missile only looks at the target,
not the trajectory. If the missile finds itself off course, it doesn't
try to get back to the old trajectory (that may be impossible) it
plans a new trajectory from where it is now to the target. (At
least, it makes the most sense to do it this way, but maybe the
missiles really have a fixed trajectory, and have to stay on it.)
The CNC should never plan a new trajectory, it has to stay
on the one defined by the toolpath program.

Jon